The present invention relates to an LSI device comprising a fully depleted silicon on insulator (FDSOI) MOS field-effect transistor (MOSFET) and a manufacturing method thereof.
There has been conventionally proposed a semiconductor device in which the film thickness of a first semiconductor active layer provided with a P channel MOSFET is made thinner than that of a second semiconductor active layer provided with an NMOSFET (refer to JP-A-1-122154, Page 2, Lower-right column, FIG. 1). There has also been a proposal that an FDSOI-MOSFET is used as a MOSFET forming an LSI device in order to achieve reduction of consumption power and high-speed in an operation of an LSI device (refer to JP-A-6-291265, Paragraph 0049, FIG. 15). An FDSOI-MOSFET can not only achieve a sub-threshold characteristic close to a theoretical limit, but also reduce sub-threshold leak current by around one figure, compared with a bulk CMOS device. Furthermore, an FDSOI-MOSFET is different from a partly depleted (PD) SOI-MOSFET in that no kink phenomena due to impact ionization occur, and is superior to a PDSOI-MOSFET in a frequency characteristic of delay time and in stability against active plate floating effect such as pass-gate leak.
As described above, an FDSOI-MOSFET can simultaneously achieve reduction of consumption power and high-speed in an operation while it has a disadvantage that short channel effect is significant. It is effective to make the film thickness of a SOI layer thinner in order to restricting the short channel effect. Thinning of the film thickness of a SOI layer, however, causes reduction of the threshold voltage of a MOSFET, so that its operation would be unstable. Therefore, it is required to adjust the threshold voltage by injecting in a channel region channel impurities at high concentration.
In a MOSFET in which a channel length is long, however, increase of channel impurities easily causes PD. PD of a MOSFET causes kink phenomena, so that a linear characteristic of an operation of a MOSFET would be lost and a circuit operation would become unstable, which causes significant difficulty in LSI designing.
The invention is for solving problems in the related art as described above. An object of the invention is to provide an LSI device capable of achieving reduction of consumption power, high-speed of an operation and stability in a circuit operation and a method of manufacturing such LSI device.